It is common for a portable electronic device such as a lap-top computer or a mobile telephone to comprise a base, which includes the device's keypad, and a lid, which includes the device's screen or user display. In this type of device, the base and the lid are connected together by a hinge section such that the user display can be hinged to lie flat against the keypad when the device is not in use. By detecting when the hinge is closed, the device is able to detect when it may safely switch to a power-saving mode. This function allows the device to conserve battery power when the device is not in use.
It is known to detect the open/closed state of this type of hinge using a mechanical sensor, such as a boss-type media detection switch or a rotary-type position detection switch. However, the use of a mechanical sensor often imposes design constraints on the electronic device and may also require that bosses be fitted to the device's exterior. A mechanical sensor often also requires extra space on the motherboard of the device for the inclusion of a detector switch.
Alternatively, the position of the hinge may be detected using a solid-state relay. For example, it is known to magnetically detect the position of a lid with a system employing a Hall Integrated Circuit. However, this type of detector requires both space on the motherboard of the device and a level of standby power. In addition, magnetic switches of this type are liable to interfere with other types of sensor which may be integrated into the device, such as those employed by global positioning systems.
The use of optical proximity sensors is also known. However the surfaces of a proximity sensor's emitter and receiver must be kept clean in order for the sensor to function reliably.